1. Field of the Invention
The invention relates to a method of converting virtually concatenated data streams into continuous concatenated data streams, wherein the data is transmitted into containers inserted into pulse frames, a sequence of N containers is combined to form a multiframe, each container is provided with a multi frame indicator relating to its position with respect to time within the multiframe, and the virtually concatenated data streams consist of X partial streams/channels.
The invention also relates to a device for the purpose of implementing this method.
2. Description of the Related Art
During the transmission of signals to systems of the SDH-type (synchronous-digital hierarchy) digital signals are introduced into so-called “containers”. Further details on this subject are known to the person skilled in the art and are disclosed, for example, in the ITU-Recommendation G.707.
In order to increase the possible data throughput, signals are divided up into several containers which are concatenated to each other. These concatenated containers can be transmitted in a common transmission frame having an appropriate capacity.
For the purpose of concatenating containers, two methods are applied, namely contiguous and virtual concatenation. Both methods provide a contiguous concatenated bandwidth which is proportional to the number X of mutually concatenated containers and to the container size. The difference lies in the transportation between the ends of the transportation path. In the case of the contiguous concatenation method, the coupling of the containers with respect to time is maintained over the entire transportation path, whereas in the case of the virtual concatenation method, the entire signal is divided up into individual virtual containers, these individual containers are transported independently and then recombined at the end point of the transmission to form the entire signal. In the case of virtual concatenation, concatenation-specific devices are only required at the ends of the transmission path, whereas in the case of contiguous concatenation, corresponding devices must generally be provided for each network element.
The start bytes of the containers are indicated by so-called “pointers” which are positioned at predetermined points of the pulse frame. The pointers thus have a fixed position with respect to the frame alignment word contained in the transmission pulse frame and indicate the distance of the container commencement from the pointer by means of a number, e.g. between 0 and 782.
In the case of virtual concatenation, the respective pointer value for each container is used on the transmission-side, but during transmission it is possible for different propagation times for the (sub)containers to occur which are caused, for example, by means of network elements in the transmission path. At the end of the virtually concatenated transmission, such propagation time differences are equalized. This is described in EP 0 429 888 B1 with respect to concatenating subsystem units for bit rates of an intermediate hierarchical order.